Abstract

The rhizosphere is teemed with organisms that coordinate their symbioses with plant roots through chemical signals. Chemicals also mediate associations between roots of different plants; the most obvious being those between parasitic Orobanchaceae and their plant hosts. These parasitic plants use specific molecules provided by host roots to initiate the development of haustoria, invasive structures critical for plant parasitism. We have taken a transcriptomics approach to identify parasitic plant genes associated with haustorium signaling. We previously identified a gene, TvPirin, which is transcriptionally up-regulated in roots of the hemiparasite Triphysaria versicolor that had been exposed to the haustorium inducing molecule 2, 6-dimethoxybenzoquinone (DMBQ). Because TvPirin shares homology with proteins associated with environmental signaling in other plants, we hypothesized that TvPirin may function in host factor recognition in parasitic plants. We tested the function of TvPirin using hairpin mediated RNA interference and found that reducing TvPirin transcripts in T. versicolor roots resulted in significantly less haustoria development. We then determined the steady state transcript levels of other root expressed genes and found that several were reduced in TvPirin silenced roots in the absence of inducer. However the up regulation of genes by DMBQ was similarly regulated in control and TvPirin silenced roots. Phylogenic investigations showed that TvPirin homologs are present in most flowering plants and we found no evidence of parasite specific gene duplication or expansion. We propose that TvPirin is a generalized transcription factor associated with the expression of several genes, some of which are involved in haustorium development.